Electrical transformer



Patented Nov. 3, 1931 2 UNITED s'rA'rEsPATEN-T OFFICE IERIDERICK H. DRAXE AND WILLIAM D. LOUGHLIN, F BOONTON, JERSEY, AB-

SIGN'ORS. BY MmNE ASSIGNMENTS', T0

NEW YORK, N. Y.,-A CORPORATION 0F DELAWARE ELECTRICAL TRANBFOBIEB 'Application led lay 5, 192B. 'lerlal No. 275,449.

t'erm refers to apparatus of the type to be hereinafter described. The invention relates more particularly to such an electrical transformer of the three-winding or threecoil type. .An object of the invention is to provide a transformer of this type so constructed and arranged that one of the coils Y has'a negligible. or in some cases substantially aoV zero. electromagnetic coupling with the other coils of the transformer, thisl coil being hereinafter referred to as the tertiary or uncoupled? coil. A further object of the invention is to provide a transformer of the foregoing tvpe in which the primary and secondary windings or coils may be relatively closely coupled electromagnetically while the tertiary coil has substantially negligible electromagnetic couplingwith the primary and secondary windings. A further object of the invention is to provide a transformer of the foregoing type Ah aving a novel design. construction. and arrangement of parts. and in which all of theI coils. or forms on which the coils are woundfare mutuallv supported from each other and combined in a unitary structurey or in which one of the coil forms constitutes a common support for the forms non which they remaining coils are wound. Other obiect's of the invention will appear from the following description.

Referring now to the drawings. Figure 1 is a longitudinal cross section taken on the plane A-B through one example of an electrical transformer according to our invention. Figure 2 is an'end view of such a transformer. Figure 3 is a view showing the opposite end of such a transformer. Figure 4 is another example of a transformer construction according to our invention.

Referring now more particularly to the specific electrical transformer construction shown in Figures 1, 2 and 3 of the drawings, 2 represents a cylindrical form on which is wound a secondary coil L2 of the transformer. The form 2 is preferably made somewhat longer than the secondary winding L2, in order to supply space for supporting the tertiary coil terminal lugs, mounting brackets and so forth. Within the form 2, and supported therefrom by a suitable supporting means 4, is another cylindrical form, 1. on which is wound a primary winding L1. The primary form, 1.I is preferably only so much smaller in diameter than the secondary form, 2, as is necessary to reduce capacity couplings to negligible values, while permitting rela.- tively close magnetic coupling between coils L1 and L2. The primary form is also considerably shorter in the direction of its principal axis than the secondary form 2, so that while the primary winding may extend substantially the whole distance under the secondary winding, the primary form does vnot extend substantially beyond the secondary winding. In the opposite end of the secondary form to that in which the primary form is arranged, is mounted a tertiary form, 3, on which is wound the tertiary coil L3. This form, 3, is mounted with its axis at'right angles to the axes of the forms 1 and Q, and the coil L3 is therefore at right angles to the coils L1 and L2. The tertiary winding L3 also extends substantially equally on either side of the axis of the primary and secondary windings. The coil L3 accordingly has negligible electromagnetic coupling with the coils L1 and LLL, due to this structure and geometrical arrangement.

The forms onwhich the'several coils are wound may suitably be made of cardboard tubing impregnated with a phenolic resin. or may be composed of laminated tubing impregnated with such a resin, and made in a4 manner well understood in the phenolic resin art. For this purpose it is preferable to employ a phenolic resin having as low a dielectric loss as possible, and also having the desired insulating properties. Shellac or other insulating materialsmay, of course, be suitably employed in lieu of a phenolic resin,

RADO BPORATION 0F AMERICA, 0F

when desired. The form 3, which is supported Jfrom the i'orm 2, with their axes at right angles, may be either a. right circular cylinder of such length as to make a force fit inside the form 2, or a cylinder having its ends of the proper curvature to fit within the cylindrical iorm 2. For example, in one construction which we have successfully' employed, form 3 is made Yfrom a Wooden plug and is tirst turned down to the proper diameter for the coil L3, and is then turned down around an axis perpendicular to the axis of the coil, so that its ends have the form of cylindrical surfaces of the same diameter as the inside of the cylindrical form 2. This Wooden plug may then be impregnated with a suitable insulating compound, such as paratiin, hallowax, phenolic resins, or other substances, and is Wound With the coil La. An alternative arrangement. is to make the form L3 4from a cardboard or laminated tube or cylinder impregnated with a phenolic resin, and to shape the ends of this cylinder to the interior diameter of the form 2 by fitting a cylindrical Wooden plug inside of the form 2, turning the Whole down on a lathe, and knocking out the Wooden plug so as to leave merely a tubular form of the proper diameter, length, and end-curvature.

Various methods of supporting the form l inside of, and coaxially with, the form 2 are suitable for use according to our invention. We have found that one ot the simplest and most satisfactory supporting means is to insert a small screw-holt through the Jforms 1 and 2, and to position over this bolt, and between the forms` a small. insulating Washer or collar of Which the length is equal to the difference between the outer radius of the form 1 and the inner radius of the form 2. Forms l and 2 may then be clamped together by tightening a nut upon this bolt, and due to the presence of the washer over the bolt betiveen the forms, the forms will be concentrically positioned. Obviously several such supporting means may be employed if required. ln particular we prefer to employ three such supporting means arranged approximately l2()O apart.

Connections to the coils LI and L2 may be made in any desired manner, but we have found that one suitable method is to punch metal eyelets into the forms l and 2at different positions. le may then solder the leads from the coils to tnese eyelets. which preferably have metal connectors or terminal lugs 5 associated with them in av convenient. manner, for example, clamped between the eyelet and the form. Mounting brackets, 6. may also be attached to either otl the forms in any convenient manner, torexample, to the extended part ot secondary form 2, as shovvn.

An alternative transformer construction, according to our invention, is shown in Figure 4, in which the primary form l is extended with respect to the secondary form 2. In this construction the tertiary torni, 5, is supported from the primary torni rather than from the secondary form as shown in Figures 1 3 inclusive. The supporting means, 4, may be the same as those described above. The terminal lugs, 5, mounting brackets, 6, and so forth, are, in this case, applied to thc extended primary torni, as shown, rather than to the secondary form as in the construction ot Figures l-B.

In connection with both the construction 'it Figures l-3 and that of Figure 4, it should also be understood that the primary and secondary windings may he interehanged; i. e., in the construction of Figures l-f the primary coil may be Wound on the outer form, 2, and the secondary coil Wound on the inner "form, l; While in the construction of Figure i the primary coil may also be wound on the outer form 2, and the secondary coil Wound on the inner form 1.

Ve prefer to extend the primary winding of the transformer, in constructions according to our invention, along substantially the full length ofthe secondary, even though the primary contains fewer turns and is usually composed of smaller wire than the secondary, in order that the self-inductance of the primary may be kept down to approximately as low a value as is practical While maintaining a given mutual inductance betvveen primary and secondary. Thus is preferably what may or s aced wound.

e claim:

l. An electrical transformer for use at radio frequencies, comprising a pair of cylindrical forms of insulating material, one of which is substantially longer than the other, means connecting said forms to retain the same in coaxial alinement and with the shorter forni in transverse alinement with one end portion of said longer form, a third cylindrical form of insulating material supported on the longer of said cylindrical forms and at the portion thereof which extends beyond said shorter cylindrical form, the axis of said third form being at right angles to the axis of said other forms, coils Wound upon each of said pair of forms, and a third coil wound upon said third form to have substantially negligible electrom gnetic coupling with the other coils.

2. An electrical transformer for use at radio frequencies, comprising a pair ot cylindrical forms of insulating material and of unequal length, means connecting said forms to retain the same in coaxial alinement and be termed extended with the shorter form in transverse alinement Withone end port-ion of the longer form, a coil wound upon said shorter form to oecup)v substantially the entire length thereof, a coi] Wound upon the longer t'orm and substantially coextensive with said first coil, a third the primary winding cylindrical .torni arranged at right angles to said cylindrical forms and supported hy the longer oi said forms at the portion thereof which extends beyond said shorter form, a coil wound upon said third form to have substantially negligible electroi'nalnctic coupling vwith said lii'st coils, and terminals for Said coils carried by said longer form at the end portion thereof which extends beyond said third form.

An electrical transformer of the herein described type. comprising a cylindrical secondary torni having a secondary winding occupying' a portion thereof; a shorter cylindrical primary form of less diameter than said secondary form, arranged. concentrically with and inside of said secondary form and supported therefrom, said primary form having thereon a primary Winding extending under at least a portion of said secondary winding; a tertiary form mounted with its axis substantially at right angles to the axis ot said secondary form, said tertiary form being mounted in the portion of said secondary form not occupied by said primary form and being supported from said secondary form, said tertiary form having a tertiary coil wound thereon; and means interconnecting said forms to constitue a fixed unitary assembly in which said primary and ter* tiary forms are su ported from said secondary form and in w ich said forms and windings are so proportioned and arranged that said tertiary coil has substantially negligible electromagnetic coupling with said secondary coil.

4. An electrical transformer for use as an nterstage coupling at the output of a balanced radio frequency amplifier stage, comprising a cylindrical secondary form having a closelywound secondary winding occupying a portion thereof; a shorter cylindrical primary form of less diameter than said secondary form arranged concentrically With and inside of said secondary form and supported therefrom, said primary form having thereon a primary winding of fewer turns than said sccoiidary Winding. said primary winding' extendineT under and occupying substantially the same winding space as said secondary winding; a tertiary form mounted with. its axis substantially at right angles to the axis of said secondary form, said tertiary form being mounted in the portion of said second* ary form not occupied by said primary form and being supported .from said secondary form, said tertiary form haring a. tertiary coil wound thereon in such a manner as to extend substantially equally on either side of the axis of said secondary Winding; said elec trical transformer constituting; a unitary asA sembly in which said primary and tertiary' forms are each supported from said second-r` ary form and in which said windings' and loi-ms are so proportioned and arranged that said tertiary coil has substantially negligible electromagnetic coupling with said second-- ary coil, terminals carried by said secondary orin` a pair ci said terminals being connected to the respective terminals of the primary Winding, ay second pair ot terminals being connected respectively to terminals ot the secondary and tertiary windings, and a fifth terminal being connected to the other terminals of said secondary and tertiary Wind ings.

ln testimony whereof we aix our sivnatures.

FREDERICK H. BRAKE. VILLIAM D. LOUGHLXN. 

